call.hpp

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#ifndef BOOST_PP_IS_ITERATING
    ///////////////////////////////////////////////////////////////////////////////
    /// \file call.hpp
    /// Contains definition of the call<> transform.
    //
    //  Copyright 2008 Eric Niebler. Distributed under the Boost
    //  Software License, Version 1.0. (See accompanying file
    //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

    #ifndef BOOST_PROTO_TRANSFORM_CALL_HPP_EAN_11_02_2007
    #define BOOST_PROTO_TRANSFORM_CALL_HPP_EAN_11_02_2007

    #include <boost/proto/detail/prefix.hpp>
    #include <boost/preprocessor/cat.hpp>
    #include <boost/preprocessor/facilities/intercept.hpp>
    #include <boost/preprocessor/iteration/iterate.hpp>
    #include <boost/preprocessor/repetition/enum.hpp>
    #include <boost/preprocessor/repetition/repeat.hpp>
    #include <boost/preprocessor/repetition/enum_params.hpp>
    #include <boost/preprocessor/repetition/enum_binary_params.hpp>
    #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
    #include <boost/ref.hpp>
    #include <boost/utility/result_of.hpp>
    #include <boost/proto/proto_fwd.hpp>
    #include <boost/proto/traits.hpp>
    #include <boost/proto/transform/impl.hpp>
    #include <boost/proto/detail/dont_care.hpp>
    #include <boost/proto/detail/as_lvalue.hpp>
    #include <boost/proto/detail/poly_function.hpp>
    #include <boost/proto/detail/suffix.hpp>

    namespace boost { namespace proto
    {
        /// \brief Wrap \c PrimitiveTransform so that <tt>when\<\></tt> knows
        /// it is callable. Requires that the parameter is actually a
        /// PrimitiveTransform.
        ///
        /// This form of <tt>call\<\></tt> is useful for annotating an
        /// arbitrary PrimitiveTransform as callable when using it with
        /// <tt>when\<\></tt>. Consider the following transform, which
        /// is parameterized with another transform.
        ///
        /// \code
        /// template<typename Grammar>
        /// struct Foo
        ///   : when<
        ///         unary_plus<Grammar>
        ///       , Grammar(_child)   // May or may not work.
        ///     >
        /// {};
        /// \endcode
        ///
        /// The problem with the above is that <tt>when\<\></tt> may or
        /// may not recognize \c Grammar as callable, depending on how
        /// \c Grammar is implemented. (See <tt>is_callable\<\></tt> for
        /// a discussion of this issue.) You can guard against
        /// the issue by wrapping \c Grammar in <tt>call\<\></tt>, such
        /// as:
        ///
        /// \code
        /// template<typename Grammar>
        /// struct Foo
        ///   : when<
        ///         unary_plus<Grammar>
        ///       , call<Grammar>(_child)   // OK, this works
        ///     >
        /// {};
        /// \endcode
        ///
        /// The above could also have been written as:
        ///
        /// \code
        /// template<typename Grammar>
        /// struct Foo
        ///   : when<
        ///         unary_plus<Grammar>
        ///       , call<Grammar(_child)>   // OK, this works, too
        ///     >
        /// {};
        /// \endcode
        template<typename PrimitiveTransform>
        struct call : PrimitiveTransform
        {
        };

        /// \brief Either call the PolymorphicFunctionObject with 0
        /// arguments, or invoke the PrimitiveTransform with 3
        /// arguments.
        template<typename Fun>
        struct call<Fun()> : transform<call<Fun()> >
        {
            /// INTERNAL ONLY
            template<typename Expr, typename State, typename Data, bool B>
            struct impl2
              : transform_impl<Expr, State, Data>
            {
                typedef typename boost::result_of<Fun()>::type result_type;

                result_type operator()(
                    typename impl2::expr_param
                  , typename impl2::state_param
                  , typename impl2::data_param
                ) const
                {
                    return Fun()();
                }
            };

            /// INTERNAL ONLY
            template<typename Expr, typename State, typename Data>
            struct impl2<Expr, State, Data, true>
              : Fun::template impl<Expr, State, Data>
            {};

            /// Either call the PolymorphicFunctionObject \c Fun with 0 arguments; or
            /// invoke the PrimitiveTransform \c Fun with 3 arguments: the current
            /// expression, state, and data.
            ///
            /// If \c Fun is a nullary PolymorphicFunctionObject, return <tt>Fun()()</tt>.
            /// Otherwise, return <tt>Fun()(expr, state, data)</tt>.
            ///
            /// \param expr The current expression
            /// \param state The current state
            /// \param data An arbitrary data

            /// If \c Fun is a nullary PolymorphicFunctionObject, \c type is a typedef
            /// for <tt>boost::result_of\<Fun()\>::::type</tt>. Otherwise, it is
            /// a typedef for <tt>boost::result_of\<Fun(Expr, State, Data)\>::::type</tt>.
            template<typename Expr, typename State, typename Data>
            struct impl
              : impl2<Expr, State, Data, is_transform<Fun>::value>
            {};
        };

        /// \brief Either call the PolymorphicFunctionObject with 1
        /// argument, or invoke the PrimitiveTransform with 3
        /// arguments.
        template<typename Fun, typename A0>
        struct call<Fun(A0)> : transform<call<Fun(A0)> >
        {
            template<typename Expr, typename State, typename Data, bool B>
            struct impl2
              : transform_impl<Expr, State, Data>
            {
                typedef typename when<_, A0>::template impl<Expr, State, Data>::result_type a0;
                typedef typename detail::as_mono_function<Fun(a0)>::type mono_fun;
                typedef typename boost::result_of<mono_fun(a0)>::type result_type;
                result_type operator ()(
                    typename impl2::expr_param   expr
                  , typename impl2::state_param  state
                  , typename impl2::data_param   data
                ) const
                {
                    return mono_fun()(
                        detail::as_lvalue(typename when<_, A0>::template impl<Expr, State, Data>()(expr, state, data))
                    );
                }
            };

            template<typename Expr, typename State, typename Data>
            struct impl2<Expr, State, Data, true>
              : transform_impl<Expr, State, Data>
            {
                typedef typename when<_, A0>::template impl<Expr, State, Data>::result_type a0;
                typedef typename Fun::template impl<a0, State, Data>::result_type result_type;
                result_type operator ()(
                    typename impl2::expr_param   expr
                  , typename impl2::state_param  state
                  , typename impl2::data_param   data
                ) const
                {
                    return typename Fun::template impl<a0, State, Data>()(
                        typename when<_, A0>::template impl<Expr, State, Data>()(expr, state, data)
                      , state
                      , data
                    );
                }
            };
            /// Let \c x be <tt>when\<_, A0\>()(expr, state, data)</tt> and \c X
            /// be the type of \c x.
            /// If \c Fun is a unary PolymorphicFunctionObject that accepts \c x,
            /// then \c type is a typedef for <tt>boost::result_of\<Fun(X)\>::::type</tt>.
            /// Otherwise, it is a typedef for <tt>boost::result_of\<Fun(X, State, Data)\>::::type</tt>.

            /// Either call the PolymorphicFunctionObject with 1 argument:
            /// the result of applying the \c A0 transform; or
            /// invoke the PrimitiveTransform with 3 arguments:
            /// result of applying the \c A0 transform, the state, and the
            /// data.
            ///
            /// Let \c x be <tt>when\<_, A0\>()(expr, state, data)</tt>.
            /// If \c Fun is a unary PolymorphicFunctionObject that accepts \c x,
            /// then return <tt>Fun()(x)</tt>. Otherwise, return
            /// <tt>Fun()(x, state, data)</tt>.
            ///
            /// \param expr The current expression
            /// \param state The current state
            /// \param data An arbitrary data
            template<typename Expr, typename State, typename Data>
            struct impl
              : impl2<Expr, State, Data, is_transform<Fun>::value>
            {};
        };

        /// \brief Either call the PolymorphicFunctionObject with 2
        /// arguments, or invoke the PrimitiveTransform with 3
        /// arguments.
        template<typename Fun, typename A0, typename A1>
        struct call<Fun(A0, A1)> : transform<call<Fun(A0, A1)> >
        {
            template<typename Expr, typename State, typename Data, bool B>
            struct impl2